Identification

Description

Valves are lanceolate in larger specimens to elliptical at the small end of the size range. The apices are narrowly to broadly rounded. The axial area is narrow and linear and extends onto the valve margins at the apices. The central area is oval in large valves, becoming linear-lanceolate in smaller valves. The raphe is filiform with expanded central fissures. The terminal raphe fissures are deflected to the same side. The striae are punctate and radiate. In the central valve, several striae are short do not extend from the central area to the valve margin. The stria density increases slightly towards the apices. The external expressions of the areolae are oval, except at the central area where they are elongated in the transapical axis. The areolae bordering the central area are elongated to a greater extent than the other areolae (SEM). Internally, the areolae are slightly elongated. Internally, the raphe slit is narrow at the proximal and terminal fissures. Helictoglossae are reduced.

Autecology

Original Description

Navicula cocconeiformis, Greg. MS. Pl. IX. fig. 6.
Length .0008" to .0011".
Navicula nugax, W. Sm. MSS.
A new species, somewhat similar in outline to Achnanthidium flexellum, with striae so fine that I have not succeeded in resolving them. I find that this species has been known for above a year to Professor Gregory, who had both sketched and named it previous to my detection of it in the Braemar gatherings. He had obtained it from Elchies and various other places in Banffshire, and latterly from Loch Leven.

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Responses

The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Cavinula cocconeiformis from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)STRAHLER = distribution plot of the Strahler Stream Order SLOPE = stream reach gradient (degrees)W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.PHSTVL = pH measured in a sealed syringe sample (pH units)log_COND = log concentration of specific conductivity (µS/cm)log_PTL = log concentration of total phosphorus (µg/L)log_NO3 = log concentration of nitrate (µeq/L)log_DOC = log concentration of dissolved organic carbon (mg/L)log_SIO2 = log concentration of silicon (mg/L)log_NA = log concentration of sodium (µeq/L)log_HCO3 = log concentration of the bicarbonate ion (µeq/L)EMBED = percent of the stream substrate that is embedded by sand and fine sedimentlog_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.

Cavinula cocconeiformis

Valves are lanceolate to elliptical with narrow to broadly rounded apices. The central area is oval to linear-lanceolate and bordered by a row of elongated, distinct areolae. The proximal raphe fissures are expanded. The striae are punctate, radiate and in the center part of the valve, several striae are do not extend from the center...